Diversity of Living Organisms - Kingdom Animalia (Salient features of Non-chordates and Chordates)

Levels of Organization: Animals exhibit different levels ranging from $Cellular$ (e.g., Porifera) to $Tissue$ (e.g., Coelenterata), $Organ$ (e.g., Platyhelminthes), and $Organ-System$ levels (e.g., Annelida to Chordata).

Symmetry: Animals are categorized as $Asymmetrical$ (cannot be divided into equal halves), $Radial$ (any plane through the center divides the body into identical halves, e.g., $Coelenterates$, $Ctenophores$), or $Bilateral$ (only one plane divides the body into identical left and right halves).

Germ Layers: $Diploblastic$ animals have two layers ($Ectoderm$ and $Endoderm$) with an undifferentiated $Mesoglea$ in between. $Triploblastic$ animals possess a third germinal layer, the $Mesoderm$.

Coelom: A fluid-filled cavity between the body wall and the gut wall. Types include $Acoelomates$ (absent), $Pseudocoelomates$ (mesoderm as scattered pouches, e.g., $Aschelminthes$), and $Eucoelomates$ (true cavity lined by mesoderm).

Non-Chordates: Lack a $Notochord$. Phyla include $Porifera$ (canal system), $Cnidaria$ (cnidocytes), $Platyhelminthes$ (flame cells for excretion), $Annelida$ (metamerism), and $Echinodermata$ (water vascular system).

Chordates: Defined by four key features: (1) $Notochord$ presence, (2) $Dorsal\ hollow\ nerve\ cord$, (3) $Paired\ pharyngeal\ gill\ slits$, and (4) $Post-anal\ tail$.

Differences in Circulatory and Nervous Systems: In Non-chordates, the heart is $Dorsal$ (if present) and the nerve cord is $Ventral$ and $Solid$. In Chordates, the heart is $Ventral$ and the nerve cord is $Dorsal$ and $Hollow$.